Yes, the power to classify, or declassify, is in the hands of the president. Voters have the ability to vote the president out if they don’t like their decisions and congress/senate can remove president with super majority in senate after impeachment. Those are the only checks on declassification/classified.
I remember Comey himself classified the memos he typed up in the limo right after he spoke with President Trump...specifically naming Flynn saying the President wanted Comey to leave Flynn alone. Comey said he took it as an order.
Comey was setting up the President.